1. Field of the Invention
The invention generally relates to fluidic devices for chemical analysis.
2. Description of the Relevant Art
The principles of two-dimensional (2-D) and three-dimensional (3-D) microfluidic paper analytical devices (μPADs) have been described by various research groups and a number of interesting applications have been reported. Briefly, for 2-D μPADs, microfluidic channels and reservoirs are fabricated by patterning channel walls on chromatography paper using a liquid-impermeable material, such as photoresist (PR) or wax. Aqueous solutions are then driven along the hydrophilic paper channels by capillary action. For 3-D μPADs, individual layers are patterned sequentially by photolithography and then stacked using double-sided tape. Holes are punched in the tape using a laser cutter, and the resulting holes are filled with cellulose powders or are compressed to provide vertical connections between adjacent layers. The results of an analysis are determined using colorimetric detection on one of the two surface layers.
The 3-D μPADs show great promise for applications such as power-free, point-of-care detection and diagnosis, particularly in underdeveloped or remote areas. However, as presently practiced, 3-D device fabrication requires a photolithographic step for each layer and then laser cutting of vias to establish fluidic connections between layers. Moreover, assembly of the device using double-sided tape is irreversible so that only the surface layer can be used for colorimetric detection. The approach we describe addresses these points.